Process for the production of tin from ores thereof



June 30, 1925. 1,544,198

I E. B. THORNHILL PROCESS FOR THEPRODUCTION 0F TIN FROM ORES THEREOF Filed Dec. 14', 1921 54 I w/l, 1/ /,l J

' INVENTOR. 1 EOW/N 5. 73a/e/vfl/LL.

BY 46 I 62 I TTORNEY a; 7 a 9 57 15 A Patented June 30, 1925.

UNITED STATES PATENT OFFICE.

EDWIN B. THORNHILL, OF HU'RLEY, NEW MEXICO, ASSIGNOR TO THO'RNHILL-ANDER- SON COMPANY, OF MUSKOGEE, OKLAHOMA, CORPORATION OF OKLAHOMA.

FBOCESS FOR THE PRODUCTION OF TIN FROM ORES THEREOF.

Application filed. December 14, 1921. Serial No. 522,292.

To gll whom. it may concern; i

. Be it known that I, EDWIN B. Ti-IORNHILL, a citizen of the United States, residing at Hurley, in the county of Grant, State of New Mexico, have invented a new and useful Process for the Productionof Tin from Ores Thereof, of which the following is a specification.

This invention relates to the production of metallic tin from tin ores such as cassiterite, or tin ore concentrates, or tin-bearing products and the main object of the invention is to provide for production of the mineral from such ores more economically and efiiciently than can be effected with the processes now in use. A further object of the invention is to carry out the reduction of the metallic tin in such manner as to avoid slugging. and to thereby obviate the loss of tin which has been incident to the ordinary furnace operations in'which a considerable portion of the tin passes into the slag, requiring reworking of the slag to recover the tin content thereof. A further object of the invention is to enable the reduction process to be carried out at relatively low temperature thereby effecting economy in operation due to saving of fuel and to saving of wear and deterioration of the furnace parts, such as results from the use of the high temperatures occurring in the processes now in operation. Another advantage of such operation at low temperature is that it reduces to a minimum the amount. of alloy of iron and tin produced in the operation.

Another object of the invention is to effect the reduction and collection of the metallic tin in such manner that liquation of the tin is effected by same operation and the same apparatus as the reduction on the melting of the tin.

The process may be carried out in various forms of apparatus; a suitable apparatus being illustrated in the accompanying drawings, wherein K Fig. 11s a horizontal section on line 1-1 in Fig. 2 of a rotary hearth furnace adapted for carrying out the invention;

Fig. 2 is a vertical section thereof on line 2-2 in Fig. 1;

Fig. 3 is a vertical section on line 3-3 in Fig- 1.

The furnace shown in the drawings comprises a rotary hearth 1 mounted to rotate on a vertical axis and a furnace casing or inclosure 3, which extends over and around said hearth to form a reducing chan'iber 4: above the hearth. Said furnace casing is here shown as having an arch shaped roof, butit may be of any suitable form and may be constructed of any suitable material, for example, ordinary brick lined with lircbrick.

The hearth 1 may be rotatably mounted in any suitable manner, being, for example, supported on roller bearings comprising an annular track 5 on the bottom of the hearth running on an annular series of rollers 6, which in turn travel on an annular stationary track 7. to a suitable spider 8 for guiding the same. In order to properly center the hearth, a central hearing may be provided therefor, comprising a stationary bearing 9 within which rotates a bearing sleeve 10- extending downward from the hearth. Suitable means are provided for rotation of the hearth, the means shown for this purpose consisting of a driving'bevel gear wheel, or pinion 12 engaging a; bevel gear ring 13, secured to the bottom of the hearth, said driving bevel gear 12 being carried by adriving shaft 14, operated in any suitable manner. The hearth 1 is formed with a, metal bottom 16, having a raised flange 17 around the same to form a pan in which is supported a bed 18 of suitable refractory material, such as brasque, the top of said bed being concave, so as tocause melted metal to drain to a central funnel 19, leading to a vertical passage 20, in the bearing sleeve 10 aforesaid.

A feed chute 23 extends downwardly through the roof of the furnacecasing so as to discharge the ore, together with the reducing agent, on to the rotary hearth, preferably near the center thereof, the ore and reducing agent being fed to this chute by any suitable means, for example, by a screw feed device 24, feeding the material from a hopper or bin 25, and operated by a suitable driving means 26'.

Stationary .rabbling devices are provided for moving, agitating and turning over the material on the rotary hearth. Two rabbling devices are shown herein it being understood that any desired number may be used. Each of said rabbling devices com prises a tube or hollow arm 27 extending through the side wall of the furnace casing The rollers 6 may be connected ble blades extend from the supporting members 27 down to the top of the material supporting bed so as to penetrate or extend into and through the body of the ore and reducing agent supported on said bed and to continually stir the same as such body is carried around by the motion of the rotary hearth; the obliquity of these rabble blades also enabling them to act as pushers for forcing the'material being treated radially outward on the rotary hearth and eventually discharging it from the outer edge of the hearth. The two rabbling devices described are shown as diametrically opposite and the,

rabbling plates thereon as arranged at intermediate radial distances in the case of the opposite devices, so that the action of each rabble blade on one armpushes the material outward in position for operation thereon by the corresponding rabble blade of the opposite arm, and the rabbling device being fixed, the material is finally pushed off ofthe hearth at a definite position adjacent to the rabbling .device having the outermost rabbling blade, and at this point of dis- .charge a collecting hopper 38'is provided to receive the material so discharged and conduct it through a chute 39 to an outlet conveyor 40. Said outlet conveyor is shown as a screw conveyor mounted in a horizontal tube '41, which is provided with a water jacket42, having. inlet and outlet connectlons 46 and 47 for cooling the conveyor tube, so as to reduce the temperature of the residual material sufliciently to prevent re oxidatlon of the tin contained therein when such material is finally discharged through outlet 43, near the outer end of tube 41.

-.Conveyor is operated by driving'means in any suitable manner. Rabble arms 27 are preferably mounted to slide through openings in the wall of the furnace to enable repair orggemoval thereof, each arm .27 beated inwardly or outwardly by a gear 35 on the carrier engaging with a rack 36 on said track, said gear 35 being manually operated by a crank 37. 4

To prevent access of external air through the joint between the rotary hearth and the furnace casing, said hearth is preferably mg, for example, mounted on a carrier sliding on a horizontal track 34 and operprovided with a depending annular flange 48 running in-an annular trough 49 extending from the side wall of the furnace casing, said trough being packedv with finely divided solid heat resistant material, such as sand or powdered coke, to form a seal for the joint. The rotary hearth is exposed to the outer air at its lower surface, so that" chamber 4 and above rotary hearth 1 so as to heat the material on the hearth by radiation, said heating means being out of contact with the material being' treated. Said heatingmeanspreferably consist of horizontal tubes of suitable resistant material extending through the side walls of the furnace, said tubes being openat one end for reception of burners 53 and opening at the other end into an outlet chamber 54' communicating with a stack 55. Said heating tubes 52 may consist of any suitable-refractory material, preferably material 'of good thermal conductivity, for example, carborundum, or similar. material, and are supported from the roof of the furnace casing in any suitable manner, for example, by passing through blocks 56 which interlock with one another and extend across the furnace chamber 1n the form of an arch. My process of t1n recovery may be carried out in the above described apparatus in the following manner. 7 j

The furnace is prepared for operation by providing on the'bed 18 a layer of heat resistant material indicated at 58 forming a pervious bed or support for the charge. For

this purpose, carbon, such as powdered coke or charcoal in a suitable state of division may be'used, but I prefer to make this 'pervious bed of an alloy of iron and tin of sufficient porosity to enable the melted tin to percolate through it, such alloy of iron and tin may be produced in suflicient amount in carrying out the process to form such a bed. Said alloy contains, for example, about 20 per cent iron and 80 per cent tin and does not melt under the heat of the reducing operation and serves the purpose not only of supporting the'charge while permitting percolation of the melted tin therethrough, but also acts'as a liquating v 1 agent as hereinafter described.

The ore,-consisting, for example, of 'cassiterite, infa suitable state of division, for example, about, 28 mesh is mixed with carbonaceous material preferably ground coke, charcoal, or coal which has been subjected to partial distillation to remove moisture and some of the volatile hydrocarbon constituents thereof, and the resulting mixture is supplied from the feed means 25 and the chute 23 to the reducing chamber of the furnace, and is deposited on the rotary hearth 1 near the center thereof. In the ro tation of the hearth, the mixture of ore and carbonaceous material constituting the reducing agent is distributed over the bed of the hearth and gradually advanced or moved outwardly in a radial direction and in passing over the hearth in this manner is subjected to heat by radiation from the heating tubes or means 52 which are heated by the burner 53 or otherwise, in such manner as to raise the temperature of the charge by heat radiated from such tubes sufficiently to cause a reducing operation to take place; the carbon of the carbonaceous material or reducing agent combining with the oxygen of the ore to form carbon monoxide with more or less carbon dioxide, and forming 'metallic tin. The reducing operation is effective at a temperature of about 1000 C. and the metallic tin liberated from the ore as above described is at sufliciently high temperature to be in fluid condition and "the major portion (about 80 per cent) of the metallic tin inthe ore collects in liquid form and percolates through the pervious supporting bed to the outlet 20 which delivers it by means of a chute 57 to a suitable receiver, such chute and receiver being preferably maintained in sufiicientl'y heated condition to retain the tin in melted state, the tin being ladled from said receiver and cast into pigs in the usual manner. The tin so recovered is herein referred to as primary tin. In passing through the porous mass of tin-iron alloy forming the bed on'which the charge rests, the melted tin is subject to liquation; so that the primary tin is substantially 'pure. The remainder of the tin is contained in the scoria or residue remaining on the hearth and is mostly in the form of grains, pellets or slugs mixed with residual carbon and gangue, forming scoria; this portion of the tin being generally combined with more or less iron, the proportion of iron combined with the tin being greater in the case of the smaller grains or pellets. By the action of the rabbles on the material carried by the rotating hearth, such material is continually broken up and permanent agglomeration or adhesion of the scoria particles is thereby prevented and the residual material comprising such scoria, including residual car: bon and gangue, as well as all the tin which does not percolate through to the outlet 20 is eventually discharged by the action of rabbles at the discharge chute 39 and is delivered at the outlet 43 at a temperature sufliciently low to prevent reoxidation of the tin.

This scoria which is continually or intermittently removed from the furnace as described, is preferably further treated for recovery for the tin content thereof. I have found that the larger pellets or slugs of metallic tin content in this scoria product is of substantially the same purity as the metallic tin which percolates through the porous bed as above described. Such pellets or larger particles of tin are preferably separated from the remainder of the mass and melted up with the primary tin. Such separation ot' the larger pieces of tin from the scoria may be effected in any suitable manher, by screening or otherwise. I prefer. however, to treat the mass of scoria in the following manner: Either before or after screening, the scoria is subjected to crushing and blowing action; for example, in amill hzwing a circulating air current for carrying ofi' dust from the mill and separating fines in a collector. Such mills are now in common use for crushing material and separating the fines from the crushed material. The coarse, material which is not carried off by the air current, consists in this case of tin pellets which are of varying size and contain an amount of iron increasing from one-half to 20 per cent as the pellets decrease in size. The larger pellets decrease in size. The larger pellets if .not already separated are removed from the rest of the tin so recovered; for example, by screening, and ore melted with the primary tin and the remainder, consisting of an alloy of tin and iron may be returned to the furnace either as a separate charge or along with the regular charge, or to a separate furnace, the furnace in that case operating as a liquating furnace for separating the pure tin from the tin iron alloy. The fines which are blown off" from the scoria in the above described crushing operation are collected as dust, and contain tin grains mixed with re-- sidual carbon, ash, and gangue, the tin content thereof being alloyed with iron as above, stated. This product may also be returned to the furnace or treated in a separate furnace of similar character.

On account, however, of the fine state of division of the tin, this product is advantageously used in the manufacture of tin compounds; for example, stannic chloride, by acting on the same with chlorine either directly or through the action of stannic chloride which acts on the tin to form stannous chloride, the latter then being converted to stannic chlorideby the action of chlorine. In case it is desired to make stannic chloride a major produet, the process may be so carried out as to produce a relatively large proportion of this finely divided tin containing material. For this purpose,

" manner to remove one or more of such conit is desirable to use the carbon employed as a reducing agent in a comparatively finely divided state (ground coke or charcoal),-the ore and carbonaceous material being for example ground to a fineness of about 200 mesh, with the result that the tin is produced mainly in finely divided condition mixed with the carbon and gangue, and in a specially suitable condition for solution, or chloridization. The tin contained in the scoria may also be recovered by dissolving the same in hydrochloric acid and precipitating on zinc ore electrolytically or otherwise. Or, the tinmay be recovered from the scoria by any hydrometallurgical process. It may also be recovered in the form of oxide by moistening the scoria without separation of the residual carbonaceous material, heating the moistened scoria in a suitable apparatus to oxidize and volatilize the tin in the form of oxide which is collected by suitable collecting means such as a bag house and the product either sold as pure tin oxide, or

recharged into the furnace, the residual carbon from the heating operation being used as fuel in the process.

In case the tin ore being treated, contains any considerable proportion of impurities,

such as antimony, arsenic, bismuth and sulphur, it may be treated in any well-known stituents.

It is essential that a reducing atmosphere be maintained within the reducing chamber, sufiicient carbonaceous material being provided to insure this, the amount of carbonaceous material used being considerably in excess of that required for actual reduction of the tin ore by combination with the oxygen thereof. Sutlicient carbonaceous material is in fact provided not only to combine with the oxygen of the tin ore, but to insure the presence of a reducing atmosphere by combination with any free oxygen that may be present, and furthermore to provide for the,

- necessary-porosity of the charge at all times,

so as to give a porous spongy scoria or dross that can be readily broken up and-discharged and that permits for free percolation OfthB reduced and melted tin. If. found desirable inany' particular case, the action of the carbonaceous material as reducing agent may.

be assisted by the introduction of reducing gas, such as hydrocarbon gas or producer gas. It is desirable, however, to avoid introduction of hydrocarbons which are liableto produce smoke and for this reason if coal is used as a reducing agent it is desirable to subject'the same to a preliminary distillation so as to drive off smoke-producing volatile hydrocarbons as well as moisture. The presenceof smoke in, the reducing chamber is disadvantageous, in that it interferes with the radiation from the heating elements tothe charge on the hearth.

The action of the rabbling device above described-limits the height to which the bed of porous material can buildup on the hearth, any agglomeration or sintering or iron and tin alloy, gangue and carbon above this height being broken up by the rabbles and the resulting scoria, in a more or less finely divided condition, being eventually pushed oil of the hearth and discharged as above described.

Any other suitable apparatus may be used in carrying out the process above described; for example, the hearth .on which the material is supported may be stationary and the rabbles caused to rotate to distribute the material over the hearth and agitate and turn over the material. The ,reduced and melted tin may be drawn off at any desired part or parts of the hearth, for example, the hearth may be provided with a' plurality of holes located between the center and periphery thereof, through which the melted tin may pass to suitable receiving means,

such as an annular trough or chamber below such holes. Or, the melted tin may flow over the periphery of the hearth into the gas seal 49 which may drain to a suitable receiver. The scoria may, if desired, be discharged peripherally of the hearth, the ore being fed at or near the center of the hearth. Furthermore, the heating devices may be variously modified; for example, instead of heating the radiating tubes by combustion therein, such tubes may be heated electrically by passing current through heating elements contained in the tubes.

What I claim is:

1. The process of recovering tin from oxide ore thereof which consists in heating the ore in a reducing atmosphere together with carbonaceous. material and without fiuxing agent to such a temperature as to efi'ect reduction and melting of the tin,

without fluxing of the gangue constituent of the ore and without production of slag.

2. The process of recovering tin from oxide ore thereof, which consists in subjecting a mixture of tin ore and carbonaceous reducing agent to the action of heat in a reducing atmosphere and without addition of fluxing. agent, to such temperature as. to effect reduction and melting of the'tin' with out production, of melted slag and withdrawing and collecting reduced and melted tin resulting from said operation.

3. The process of recovering tin from exide ore thereof which consists in subjecting a mixture of the ore and carbonaceous material without flexing agent to the action of heat radiated to the said mixture from above, While said mixture is supported on a pervious bed, in such manner as to effect reduction and melting of tin without-p1o duct-ion of melted slag, whereby a portion of the reduced and melted tin is caused to in the presence of a reducing atmosphere percolate through the pervious bed and is collected thereunder and another portion of the tin together, with the carbonaceous material and gangue is caused to form a friable scoria which remains on top of said bed and is removed therefrom by mechanical operation.

4. The process which consists in supplying a mixture of tin ore and carbonaceous material on to a pervious supporting bed with a reducing chamber, radiating heat on to said mixture and maintaining a reducing atmosphere in said chamber to effect reduction and melting of the tin without production of melted slag and to cause production of a porous friable scoria containing gangue, carbonaceous material and residual tin; and subjecting the charge within the furnace to rabbling'action to distribute the same over said bed to break up such friable scoria and to discharge the scoria from the bed, collecting the scoria so discharged from the bed and collecting the primary reduced and melted tin which percolates through the said pervious bed.

5. The process which consists in subjecting a mixture of tin ore and carbonaceous reducing agent to heat in a reducing atmosphere while such ore and reducing agent are supported on a pervious bed permitting percolation therethrough of the reduced and melted tin, continually supplying ore and reducing agent to the top of said bed, continually withdrawing reduced and melted tin from below said bed and continually withdrawing from the top of the bed residual material containing tin, carbonaceous material and gangue.

6. .The process which consists in subjecting a mixture of tin ore and carbonaceous material to heat in a reducing chamber and while said tin ore and carbonaceous material are supported on a pervious bed permitting percolation therethrough of reduced and melted tin, continually feeding a mixture of tin ore and carbonaceous material to said bed and distributing said material over said bed, withdrawing reduced and melted tin from below said bed and causing residual material containing tin, carbonaceous material and gangue to be discharged from said bed.

7. The process of recovering tin from tin oxide ore which consists in subjecting a mixture of said ore and carbonaceous ma terial to heat while such mixture is distributed on a pervious bed, in such manner-as to effect reduction and melting of the tin without fluxing the gangue and to cause a portion of the reduced tin to flow through the pervious bed and be collected thereunder and another portion of the tin to form, together with carbonaceous material and gangue, a porous friable'scoria and removing such scoria from the bed.

8. The process of recovering tin from oxide ore thereof which consists in subjecting such ore to the action of a reducing agent in a reducing atmosphere, heating the ore during the reducing operation by radiation from heating surfaces, continually rabbling and turning over the ore and reducing agent during the heating operation, and removing the melted tin from the residual material.

9. The process of recovering tin from tin oxide ore which consists in'passing such ore together with a reducing agent continuously into a reducing chamber, distributing the ore and reducing agent in a shallow layer in said chamber, rabbling the me so distributcd,'subjecting such layer of ore to heat imparted to the same by radiation from above, to heat the charge of ore and reducing agent sufficiently to eifect reductionand melting of the tin and maintaining below the charge of ore and reducing agent a bed of porous material to which residues may descend for collection thereof.

10. Aprocess as set forth in claim 9 and comprising, in addition, continual removal of residual material containing residual carbon, gangue, and residual tin in finely divided condition from the said chamber and cooling such residual material.

11. The process which consists in subject} ing tin ore to a reducing and melting oper' ation while said ore is separated on a pervious bed consisting of a tin-iron alloy which is not fusible at the temperature of reduction of the tin ore and causing the reduced and melted tin to percolate through such pervious bed and to be subjected to liqua- {3051 by contact with the material of such In testimony whereof I have hereunto subscribed my name this 5th day of December, 1921.

EDWIN B. THORNHILL. 

